1. Field of the Invention
The presently disclosed subject matter relates to a method for producing entrapping immobilization pellets, an apparatus for producing entrapping immobilization pellets, and entrapping immobilization pellets, and particularly relates to a technique to eliminate fluctuation in pellet strength of entrapping immobilization pellets according to production lots, thereby increasing pellet life span.
2. Description of the Related Art
Nitrifying bacteria included in an activated sludge used for waste water treatment grow slower than common bacteria. The number of the nitrifying bacteria decreases particularly in winter when a water temperature is low, leading to a significantly lower nitrification activity. This applies to useful bacteria whose proliferative rate is low as with the nitrifying bacteria. For that reason, waste water treatment performance is improved by immobilizing microorganisms containing useful bacteria such as the nitrifying bacteria, for example, an activated sludge in pellets to increase a concentration of such useful bacteria.
A method for immobilizing an activated sludge is mainly classified into the following two methods as described in “Biseibutsu-Koteikahouniyoru Mizushori, Tantai-Koteikahou, Houkatsu-Koteikahou, Seibutsu-Kasseitanhou [Water Treatment by Microorganism Immobilization Method: Pellet Immobilization Method, Entrapping Immobilization Method and Biologically Activated Carbon Method (in Japanese)],” published by NTS Inc., (2000). One is an attachment immobilization method (or a bonding immobilization method) in which an activated sludge is naturally attached or adsorbed to an inside of a surface or pores of pellets so that bacteria in the activated sludge proliferate. The other is an entrapping immobilization method for entrapping an activated sludge within an immobilizing material.
Comparing these two types of the immobilization methods, the entrapping immobilization method activates the useful bacteria such as the nitrifying bacteria more rapidly and more stably than the attachment immobilization method does. Entrapping immobilization pellets are produced by mixing an activated sludge with an immobilizing material such as a high molecular compound to prepare a raw material solution, and polymerizing this raw material solution by a polymerization initiator into a gel, as disclosed in Japanese Patent Application Laid-Open No. 2006-333851, for example.